Pelletized explosive of trinitrotoluene prills coated with sodium and ammonium nitrat in an organic binder



United States Patent 3,304,211 PELLETIZED EXPLOSIVE 0F TRINITROTOLUENEPRILLS COATED WITH SODIUM AND AMMO- NIUM NITRATE IN AN ORGANIC BINDERRobert J. Anderson, Toronto, Ontario, and John F. Short, Willowdale,Ontario, Canada, assignors to Union Carbide Canada Limited, Toronto,Ontario, Canada, a corporation of Canada No Drawing. Filed Mar. 30,1965, Ser. No. 444,047 5 Claims. (Cl. 149-11) This invention relates tonovel explosive compositions and in particular to improved ammoniumnitrate blasting compositions-resistantto the action of Water andcapable of use in boreholes containing standing Water.

In large scale blasting operations, it has been found most effective touse loose free running granular or pelletized explosives rather thanstick explosives or explosives in rigid containers, since the use ofsuch free running blasting agents enables complete filling of theborehole, regardless how irregular, resulting in the maximumconcentration of the explosive in the borehole. However, ammoniumnitrate possesses essentially no water resistance, and therefore whensuch compositions are to be employed in Wet boreholes, particularlythose containing standing water, the ammonium nitrate must be packed ina flexible plastic bag to protect it from contacting moisture. Thedisadvantages accruing from this technique are obvious since, in thefield, such flexible plastic containers easily become ruptured or tornin handling or in insertion in the borehole. Moreover, even whenwaterproofed by one of other various methods, ammonium nitrate, beingless dense than water, segregates in a wet borehole and results in a lowefficiency explosion.

Accordingly, despite the additional expense, the more dense andwater-soluble explosives, such as trinitrotoluene, are finding greateracceptance particularly in wet borehole applications.

It is accordingly an object of this invention to provide a pelletizedfree running explosive composition.

It is a further object of this invention to provide such a free runningblasting composition which contains ammonium nitrate and sodium nitrate.It is a further object of this invention to provide such a blastingcomposition which may be readily employed in wet boreholes, even thosecontaining standing water.

The novel explosive compositions of this invention comprise pelletswhich contain a trinitrotoluene portion consisting of trinitrotolueneprills and an oxidant portion consisting essentially of ammonium nitrateand sodium nitrate which oxidant portion is admixed with a binder systemcomprised of calcium ligna sulfate and polyethylene oxide, Thetrinitrotoluene prills serve as seeds for the pelletization operation inthe manufacture of the explosive, and hence the novel pelleted explosivecompositions of this invention essentially comprise a layer of binderand oxidant, i.e., ammonium nitrate and sodium nitrate, adhered to andaround a trinitrotoluene prill.

This pelletization procedure enables production of an explosivecomposition having a density up to about 90 pounds per cubic foot, whichcomposition is also substantially water resistant. By the term waterresistant in this application is meant that the pelletized explosivescan resist both segregation of the oxidant portion from thetrinitrotoluene, and leaching of the oxidant from the pellet for as longas six days in a moisture containing environment.

To facilitate the attainment of high density in the ultimatecompositions of this invention, the trinitrotoluene prills employed toseed the pellets are preferably of high density themselves, e.g., havingan absolute density of from about 1.50 to 1.60 grams per cubiccentimeter. It

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is also preferred that the trinitrotoluene prills be essentiallyspherical in shape and uniform in size since such characteristicsfacilitate the pelletizing procedure.

To assure proper density as well as desirable explosive characteristicsthe novel pelletized explosive of this invention comprises from about 25to about 40% by weight trinitrotoluene in the form of prills ashereinbefore set forth, from about 2 to about 10% by Weight of thebinder system comprising calcium ligna sulfate and polyethylene oxide,with the remainder being comprised of the oxidant portion of theexplosive composition which oxidant por tion contains at least 50% byweight based on the oxidant portion itself of sodium nitrate, theremainder "being ammonium nitrate. The use of greater amounts ofammonium nitrate in the oxidant portion will usually result in anexplosive having an absolute density too low to serve the purposes ofthe instant invention. Furthermore, although employing more than 40% byweight trinitrotoluene in these explosives is wholly operative, sincethe cost of the finished explosive is dependent almost directly upon theamount of trinitrotoluene employed, the use of greater amounts oftrinitrotoluene is not preferred because of economic factors.

The binder system employed in the novel explosive compositions of thisinvention is present in sufficient amounts to adhere the oxidant to thetrinitrotoluene prill during the pelletization procedure and to providewater resistance, as defined above, to the composition. The binder iscomposed of from about 40 to about 70% by weight polyethylene oxide andfrom about 60 to about 30% by weight calcium ligna sulfate. In theseproportions, these binder ingredients provide an excellent pelletizingcement for producing the explosive according to this invention and alsoprovide a fuel for the overall explosive composition.

The polyethylene oxide preferably employed in this invention possesses ahigh moleucular weight having a reduced viscosity of at least 1,preferably from about 1 to as high as about 20. Reduced viscosity isdetermined from a sample containing 0.2 gram of polyethylene oxide inmillimeters of acetonitrile. These values correspond roughly topolyethylene oxide polymers having a molecular weight in the range of atleast 100,000, preferably in the range of about 100,000 to about 4 or 5million.

The pelletization operation may be effected in a standard conventionalrotating mill. The trinitrotoluene prills, the oxidant portion of theexplosive, and the binder system consisting of polyethylene oxide andcalcium ligna sulfate are premixed with a small amount of watersufficient to create a thick paste of the nitrate and the binder.Preferably, from about 10 to about 15% by weight of Water based upon theweight of the entire composition is employed. It is preferred to utilizethe nitrate portion of the composition and the binder in finely dividedform to improve the mixing of these ingredients. The pellet once formedis then dried at elevated temperatures preferably by a steam dryingoperation. In one preferred mode of operation, excess binder within thepellets is gently squeezed out to the drying operating by submitting thepellets to the motion of a non-sparking ballbearing grinder operating atrelatively low speed. This tends to improve the density of the pelletand to speed the drying operation. Excess binder removed by thisprocedure can be recovered and reutilized in subsequent batches ofexplosives. In the drying operation, essentially all the water addedprior to the pelletization is preferably removed from the prills.

By the above procedure, pellets of varying sizes may be obtained. Ofcourse, the ultimate size of the explosive pellets will be dependentupon the size of the trinitrotoluene prills used as a seed therein.Pellets ranging in size from about A to about in diameter are preferredsince their size results in a minimum of space between the pellets, andhence enables efiicient charging of boreholes. The trinitrotolueneprills should therefore be chosen accordingly.

The novel pelletized explosive of this invention may also optionallycontain a metallic fuel in an amount of up to about 20% by weight. Theinclusion of such a fuel naturally increases density, oxygen balance,and velocity of detonation, and consequently such factors must beconsidered in the selection of the fuel and the amount thereof. Suchmetallic fuel is, of course, employed in a finely divided state toprovide uniform comingling of the ingredients and is added to the otheringredients in the pelletization. Metallic fuels which are useful in theexplosives of this invention include ferrosilicon, aluminum, iron,manganese, ferromanganese, magnesium, and various magnesium alloys suchas magnesiumsilicon alloys. Inasmuch as the use of metallic fuelcontributes towards the density of the overall explosive, the additionof this ingredient concurrently implies that the minimum prescribedamount of trinitrotoluene can be employed. Hence, when such a metallicfuel is employed, it supplants in part the oxidant portion of theexplosive composition as hereinbefore prescribed.

Although the explosive of this invention, due to its free runningnature, is primarily useful in applications where it is poured directlyinto a borehole, the compositions of this invention may also be employedin conventional containers such as paper and the like.

The invention has been described in detail in the foregoingspecification, nonetheless, it will be apparent to those skilled in theart of explosive manufacture that many variations are possible withoutdeparture from the scope of the invention.

What is claimed is:

1. A pelletized explosive composition having a density greater thanwater which comprises a trinitrotoluene prill, abinder, and an oxidantportion consisting essentially of at least 50% by weight based upon theoxidant portion of sodium nitrate and ammonium nitrate, said oxidantportion and said binder being a'hered around said prills to form thepellets.

2. The pelletized explosive composition of claim 1 wherein said binderconsists essentially of calcium ligna sulfate and polyethylene oxide.

3. A pelletized explosive composition having a density greater than thatof water comprising from about 25 to about 40% by weighttrinitrotoluene, from about 2 to about 10% by weight of a binderconsisting essentially of calcium ligna sulfate and polyethylene oxideand from about to about 75% by weight of an oxidant portion consistingessentially of at least 50% by weight based upon the oxidant portion ofsodium nitrate, and ammonium nitrate, said explosive constituting apellet wherein said binder and oxidant portion are adhered around saidtrinitrotoluene prill to form a pellet.

4. The pelletized explosive composition of claim 3 which contains up toabout 20% by weight of a finely divided metallic fuel. 7

5. The pelletized explosive composition of claim 3 wherein said binderportion consists of from about 40 to about 70% of calcium ligna sulfateand from about to about 30% polyethylene oxide.

References Cited by the Examiner UNITED STATES PATENTS 3,053,707 9/1962Davis et al 149-8 3,112,233 11/1963 Friedman et a1 14911 X 3,160,53512/1964 Wells 149105 X CARL D. QUARFORTH, Primary Examiner.

B. R. PADGETT, Assistant Examiner.

3. A PELLETIZED EXPLOSIVE COMPOSITION HAVING A DENSITY GREATER THAN THATOF WATER COMPRISING FROM ABOUT 25 TO ABOUT 40% BY WEIGHTTRINITROTOLUENE, FROM ABOUT 2 TO ABOUT 10% BY WEIGHT OF A BINDERCONSISTING ESSENTIALLY OF CALCIUM LIGNA SULFATE AND POLYETHYULENE OXIDEAND FROM ABOUT 50 TO ABOUT 75% BY WEIGHT OF AN OXIDANT PORTIONCONSISTING ESSENTIALLY OF AT LEAST 50% BY WEIGHT BASED UPON THE OXIDANTPORTION OF SODIUM NITRATE, AND AMMONIUM NITRATE, SAID EXPLOSIVECONSTITUTING A PELLET WHEREIN SAID BINDER AND OXIDANT PORTION AREADHERED AROUND SAID TRINITROTOLUENE PRILL TO FORM A PELLET.